Chapter 12

Information Systems

Nell Dale • John Lewis

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Chapter Goals

• Define the role of general information systems

• Explain how spreadsheets are organized

• Create spreadsheets for basic analysis of data

• Define appropriate spreadsheet formulas using built-in functions

• Design spreadsheets to be flexible and extensible

• Describe the elements of a database management system

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Chapter Goals (cont.)

• Describe the organization of a relational database

• Establish relationships among elements in a database

• Write basic SQL statements

• Describe an entity-relationship diagram

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Managing Information

• An information system can be generally defined as software that helps us organize and analyze data

– Flexible application software tools that allow the user to dictate and manage the organization of data, and that have basic processing capabilities to analyze the data in various ways

– Two of the most popular general application information systems are electronic spreadsheets and database management systems

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Spreadsheets

• A spreadsheet is a software application that allows the user to organize and analyze data using a grid of labeled cells– A cell can contain data or a

formula that is used to calculate a value

– Data stored in a cell can be text, numbers, or “special” data such as dates

– Spreadsheet cells are referenced by their row and column designation

Figure 12.1 A spreadsheet, made up of a grid of labeled cells

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Spreadsheets

• Suppose we have collected data on the number of students that came to get help from a set of tutors over a period of several weeks

Figure 12.1 A spreadsheet containing data and computations

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Spreadsheet Formulas

• The power of spreadsheets comes from the formulas that we can create and store in cells– When a formula is stored in a cell, the result

of the formula is displayed in the cell– If we’ve set up the spreadsheet correctly, we

could add or remove tutors, add additional weeks of data, or change any of the data we have already stored and the corresponding calculations would automatically be updated

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Spreadsheet Formulas

Figure 12.1 The formulas behind some of the cells

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Spreadsheet Formulas

• Formulas can make use of basic arithmetic operations using the standard symbols (+, 2, *, and /)

• They can also make use of spreadsheet functions that are built into the software– Functions often operate on a set of contiguous

cells

• A range of cells is specified with two dots (periods) between the two cell endpoints

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Spreadsheet Formulas

Figure 12.4 Some common spreadsheet functions

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Circular References

• A circular reference can never be resolved because the result of one formula is ultimately based on another, and vice versa

Figure 12.5 A circular reference situation that cannot be resolved

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Spreadsheet Analysis

• One reason spreadsheets are so useful is their versatility

• Spreadsheet analysis can be applied to just about any topic area– Track sales– Analyze sport statistics– Maintain student grades– Keep a car maintenance log– Record and summarize travel expenses– Track project activities and schedules– Plan stock purchases

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Spreadsheet Analysis

• Another reason spreadsheets are so useful is their dynamic nature

• The dynamic nature of spreadsheets also provides the powerful ability to do what-if analysis

– What if the number of attendees decreased by 10%?

– What if we increase the ticket price by $5?

– What if we could reduce the cost of materials by half?

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Database Management Systems

• A database can simply be defined as a structured set of data

• A database management system (DBMS) is a combination of software and data made up of:– Physical database—a collection of files that contain

the data– Database engine—software that supports access to

and modification of the database contents– Database schema—a specification of the logical

structure of the data stored in the database

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Database Management Systems

Figure 12.6 The elements of a database management system

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Database Management Systems

• Specialized database languages allow the user to specify the structure of data; add, modify, and delete data; and query the database to retrieve specific stored data

• The database schema provides the logical view of the data in the database

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The Relational Model

• In a relational DBMS, the data items and the relationships among them are organized into tables

– A table is a collection of records

– A record is a collection of related fields

– Each field of a database table contains a single data value

– Each record in a table contains the same fields

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A Database Table

Figure 12.7 A database table, made up of records and fields

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A Database Table

• We can express the schema for this part of the database as follows:

Movie (MovieId:key, Title, Genre, Rating)

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Relationships

Figure 12.8 A database table containing customer data

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Relationships

• We can use a table to represent a collection of relationships between objects

Figure 12.9 A database table storing current movie rentals

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Structured Query Language

• The Structured Query Language (SQL) is a comprehensive database language for managing relational databases

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Queries in SQL

select attribute-list from table-list where condition

select Title from Movie where Rating = 'PG'

select Name, Address from Customer

select * from Movie where Genre like '%action%'

select * from Movie where Rating = 'R' order by Title

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Modifying Database Content

insert into Customer values (9876, 'John Smith', '602 Greenbriar Court', '2938 3212 3402 0299')

update Movie set Genre = 'thriller drama' where title = 'Unbreakable'

delete from Movie where Rating = 'R'

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Database Design

• One popular technique for designing relational databases is called entity-relationship (ER) modeling

• Chief among the tools used for ER modeling is the ER diagram– An ER diagram captures the important record

types, attributes, and relationships in a graphical form

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Database Design

• These designations show the cardinality constraint of the relationship

Figure 12.10 An ER diagram for the movie rental database

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Ethical Issues: Encryption

• The ability to transfer sensitive information securely from one computer to another is critical

• Secure sites protect personal information through cryptography

• Once encrypted, these messages can be deciphered only by using a key, or translator